1. Field of The Invention
This invention relates to a vulcanizable organopolysiloxane composition which is both room temperature vulcanizable and photo-vulcanizable in nature. More particularly, the invention relates to a curable or vulcanizable organopolysiloxane which has good shelf stability and is vulcanizable by UV irradiation and/or by means of moisture in air at room temperature thereby providing a cured rubber elastomer having good tensile strength. Such a composition is particularly suitable for use as a sealant, coating agent or potting agent.
2. Description of The Prior Art
A variety of room temperature vulcanizing organopolysiloxane compositions (hereinafter referred to simply as RTV siloxane composition) are known. Among these compositions, there is known a composition which comprises an organopolysiloxane having a hydroxyl group at the ends of the molecular chain along with a crosslinking agent such as methyltrimethoxysilane and an organotitanium compound or a titanium chelating compound as a catalyst. When vulcanized, this composition yields a rubbery organopolysiloxane while producing an alcohol. Thus, this composition is not corrosive without generation of any irritative odor and has been widely used as an adhesive in the fields of electric and electronic industries.
However, this de-alcoholization type of RTV siloxane composition is disadvantageous in that the vulcanizing velocity is generally low with poor internal vulcanizability and poor storage properties. When stored over a long time under water-free conditions, the composition is unlikely to be vulcanized on use. To overcome the above disadvantage, there has been proposed a composition wherein a silane compound having two alkoxy groups is added to the de-alcoholization type of RTV siloxane composition as a so-called silane-type scavenger so as to improve the storage stability and vulcanizability. Moreover, another type of de-alcoholization-type RTV siloxane composition has been proposed in Japanese Laid-open Patent Application No. 58-52351. This composition comprises a diorganopolysiloxane blocked with a hydroxyl group at the ends of the molecular chain, an alkoxysilane or its partial hydrolyzate, a guanidyl-substituted alkoxysilane of the following formula EQU [(CH.sub.3).sub.2 N]C.dbd.N(CH.sub.2).sub.3 Si(OCH.sub.3).sub.3
and an organotin compound.
With the composition to which the silane compound having two alkoxy groups is added as a silane-type scavenger, however, it will be necessary that the silane compound have highly reactive groups such as an amido group, an amino group and the like as hydrolyzable groups other than the two alkoxy groups in order to: impart good storage stability. This will bring about corrosive properties and an offensive odor. Thus, the composition cannot stand use as an adhesive in the electric and electronic industries. In order to overcome the above disadvantage, we have already proposed de-alcoholization-type RTV siloxane compositions which comprise .alpha.-silyl ester compounds highly reactive with alcohols, thereby improving the storage stability, and which are substantially free of corrosive properties and offensive odors.
However, the RTV siloxane compositions of the de-alcoholization type have been strongly demanded to increase the vulcanization speed in view of the speeding-up of the production line in the electric and electronic industries.
It is known that in contrast to condensation-type, thermal vulcanization-type and platinum addition reaction-type organopolysiloxane compositions, UV-curing or vulcanizing organopolysiloxane composition has a higher vulcanization speed mechanism. The UV vulcanization type organopolysiloxane compositions known in the art are ones which comprise, for example, a vinyl group-containing polysiloxane and a mercapto group-containing polysiloxane, both being vulcanized through photo-radical addition reaction. Such compositions are set out, for example, in Japanese Patent Publication No. 52-40384 and Japanese Laid-open Patent Application No. 60-104158. However, the compositions have the problems on the offensive odor of the mercapto group and the corrosive properties thereof. Thus, limitation is inconveniently placed on their utility.
Moreover, Japanese Patent Publication No. 53-36515 and Japanese Laid-open Patent Application No. 60-215009 propose photo-curable or vulcanizable compositions which comprise acryl group-containing polysiloxanes and sensitizers. In order to obtain rubbery elastomers, high molecular weight linear polymers have to be used. This is disadvantageous in that the amount of acryl groups positioned at terminal ends becomes relatively very small, adversely influencing the vulcanizability. In addition, the surface moieties which are in contact with air are unlikely to undergo vulcanization owing to the vulcanization inhibiting action of oxygen. Only resin-type products rather than elastomer having a relatively large amount of acryl groups have been put in practice. Thus, satisfactory rubbery elastomers have not been obtained yet.
The above-stated photocurable organopolysiloxane compositions call be vulcanized within a short time by application of UV light. In this sense, such compositions are advantageous in working or handling properties over conventional condensation-type, thermal vulcanization-type or platinum addition reaction-type compositions. However, the resultant silicone rubber elastomer exhibits poor tensile strength and is snort of shelf stability, with its application being inconveniently limited.